Extreme pressure lithium greases



EXTREME PRESSURE LITHIUM GREASES Thomas W. Martinek, Crystal Lake, Elmer W. Brennan, Dundee, and Ernest T. Fronczak, Crystal Lake, 11]., assignors to The Pure Oil Company, Chicago, Ill., a corporation of Ohio No Drawing. Filed Apr. 14, 1958, Ser. No. 728,111

6 Claims. (Cl. 252-323) The present invention relates to an improved lubricating grease composition and, more particularly, to lithium base grease compositions containing selected extreme pressure-imparting soaps which retain their extreme pressure properties on storage, and to processes of making such greases.

Lithium-base greases have found recent application in various industries for lubricating purposes. As far as the manufacture and use of grease compositions are concerned, the principal characteristics which are most important comprise consistency, drop point, yield, and storage stability. Those greases used under extreme load conditions must be fortified with extreme pressure addends in order to withstand operating conditions without breaking down or otherwise changing in characteristics. It is particularly diflicult to obtain high film strength values in lithium-base greases, but, more important, prior art lithium-base greases containing extreme pressure addends in suflicient amount to obtain high initial film strength commonly exhibit decreases in film strength as the greases age in storage and in use. The loss of film strength in extreme pressure, lithium-base greases is typified by the data in Table I below and which is found in Boner, Manufacture and Application of Lubricating Greases, p. 115, 1955:

TABLE I Effect 07 age of lithium-base E. P. Greases on T imken film strength values The above table demonstrates that film strength ordinarily decreases with time in lithium-base E.P. grease formulations, except where specific stabilizers are added, as in 3 above, to retard or eliminate such a decrease in E.P. properties.

We have now discovered that by the proper selection and processing of certain soap stocks to lithium-base E.P. greases, we can produce greases which retain their extreme pressure properties in undiminished strength over periods of up to 3 months or more. Our greases, moreover, exhibit superior yields, dropping points, shear stability and other desirable properties. It is unnecessary to add extreme pressure-stabilizing compounds to our greases in order to retain their extreme pressure properties over long periods of time.

Accordingly, it is an object of our invention to provide superiorlithium-base, extreme pressure greases and a method of preparing the same.

It is another object of our invention to provide lithiumnited States Patent base extreme, pressure grease compositions which exhibit undiminished extreme pressure properties on long storage.

It is a further object of our invention to provide a method of processing lithium-base, extreme pressure greases, so that a gel-like grease structure is produced and the extreme pressure properties are retained on storage.

It is also an object of our invention to provide lithiumbase, extreme pressure, grease formulations comprising mineral oil, lithium soaps of hydroxy acids and lithium soaps of sulfurized-phosphorized fats or fatty oils, and containing no extreme pressure-stabilizing addends, but which show undiminished extreme pressure properties on long storage.

Another object is to provide an improved process for preparing a lithium-base extreme pressure grease in which the grease is dehydrated and a soap-oil dispersion formed at a temperature such that a gel-like grease structure is produced upon cooling.

Other objects will become apparent throughout the specification and claims as hereinafter related.

In general, therefore, our invention comprises extreme pressure, lithium-base grease formulations having undiminished extreme pressureproperties on long continued storage and a method of preparing the same.

More particularly, our invention resides in lithiumbase, extreme pressure greases comprising mineral oil and mixed lithium soaps of (1) saturated hydroxy fatty acids and/or glycerides of saturated hydroxy fatty acids of carbon chain length of 12 to 22 carbon atoms and (2) snlfurized phosphorized fatty materials prepared from mono-unsaturated fats or fatty oils having acid radicals of 12 to 22 carbon atoms in chain length.

The first constituent for the lithium soap comprises glycerides of saturated hydroxy fatty acids, as stated above, having acid radicals of carbon chain length of 12 to 22 carbon atoms.

The glycerides of saturated hydroxy acids utilized in our invention are glyceryl esters of the above acids, therefore having saturated hydroxy acid radicals of carbon chain lengths of 12-22 carbon atoms. The glycerides when saponified yield lithium soaps of the above-defined hydroxy acids and free glycerol.

Fats and oils ordinarily have the'greater proportion of their fatty acids present in ester form with glycerol, rather than as free acids. This is true with hydrogenated castor oil. About of the total fatty acid present in the hydrogenated castor oil is l2-hydroxy stearic acid, substantially all of which is present in the form of glycerol ester.

The above first constituent may be in a pure or relatively pure form to minimize or eliminate formation of lithium soaps which might tend to cause, contribute to, or promote a decrease in extreme pressure properties of the grease on storage.

The second, fatty-acid-containing constituent of our grease is any one or mixture of glyceryl triesters of non-hydroxy-containing, mono-unsaturated fatty acids with 12-22 carbon atoms in the carbon chain. Lard oil is a preferred example. This oil contains chiefly glyceryl trioleate with smaller amounts of glyceryl esters of palmitic, stearic, myri'stic and linoleic acids present. Glycerides of other mono-unsaturated fatty. acids of 12-22 carbon atoms may be used in place of glyceryl trioleate and include in relatively pure form glyceryl esters of dodecylenic, palmitoleic, petroselinic, vaccenic, tariric, gadoleic cetoleic erucie acids and mixtures thereof.

The ester, oil, fat or mixture thereof, must therefor have acid radicals present before sulfurizing-phosphorizing which are mono-unsaturated and non-hydroxy-containing. The sulfurization-phosphorization may be carried out according to any conventional method utilizing either phosphorus sesquisulfide or phosphorus pentasulfide and sulfur, for example, according to the method of Whittier et al., US. Patent No. 2,211,306. Other methods, such as those disclosed in US. Patent Numbers 2,382,121, 2,483,600, 2,420,280, 2,211,231, 2,274,022, 2,352,818, 2,419,153, 2,422,206, 2,375,061, etc. are suitable. The sulfurization may be carried out alone and according to the sulfurization step in above methods set forth for the sulfurization-phosphorization procedures, that is, for example, according to the sulfurization steps of US. Patent Numbers 2,382,121, 2,483,600, 2,420,280, 2,211,306, 2,211,231, etc. The sulfurization procedure of US. Patent No. 2,451,895 may also be utilized, as may the sulfurization step disclosed in British Patent No. 704,788.

On sulfurization-phosphorization of the mono-unsaturated, non-hydroxy-containing acid radicals, the unsaturated bonds are largely, if not completely, reacted, so that the sulfuror sulfur and phosphorus-containing product should not be considered a mono-unsaturated fatty material.

The mineral oil base of our grease composition may be any one or mixture of two or more mineral oils boiling in the lubricating oil boiling range, including bright stocks and neutral oils of any suitable viscosity, and solvent extracts thereof, that is, extracts obtained by extracting mineral oils with such conventional solvents as phenol, furfural, sulfur dioxide and the like, preferably phenol. For example, the extract obtained by solvent extracting a 100 viscosity, SUS at 100 F., neutral oil with phenol may be used in the preparation of our grease, alone or in admixture with other lubricating oils. As another example, the phenol extract from the manufacture of bright stock, having API gravity of about 8.0 to 15 and viscosity at 210 F. above about 175 SUS, may be used.

The crude oils from which the base oils suitable for our use are obtained may be any conventional crudes, such as Gulf Coast, Pennsylvania, Mid-Continent, etc., and during processing to the desired lubricating oil may be subjected to any conventional treatment, such as acid refining or solvent refining.

Our process for the preparation of our lithium greases broadly may be described in the following steps: The fatty components 1) and (2) above-described are added separately or together to a reaction zone, for example, an open grease kettle, before, after or with a portion of the base oil and heated to about 190 F. or other suitably high temperature, for example 150200 F. Preferably, constituents (1) and (2) are added after the base oil has been heated to the indicated temperature. The fatty constituent (2) must be prepared before charging according to one of the above methods set forth and be present in the sulfurized-phosphorized form. On suitable agitation of the ingredients, the temperature is raised to about 200 F. and the lithium agent is added, that is, lithium hydroxide, anhydrous lithium hydroxide or lithium oxide in water, a sufficient amount being added to substantially completely convert components (l) and (2) to their respective lithium soaps. The mixture while being agitated is then raised to a critical temperature range of about 320-340 F. and maintained at that temperature for about an hour, that is, until substantially complete dehydration of the mixture has occurred. The dehydrated grease is then cut back to the desired soap concentration with additional base oil and any additional agents are added under agitation at around 240 F.

An oxidation inhibitor such as tetramethyldiaminodiphenylmethane, alphaor beta-naphthylamine, phenyl alphaor beta-naphthylamine and alpha-beta di-naphthylamine may optionally be added to our grease to prevent oxidation of the fatty components and rancidity of the grease. The oxidation inhibitor does not affect the 4 stability of the extreme pressure properties of the grease per se.

The grease is cooled after the constituents are uniformly blended and dispersed throughout the body of the grease which has a gel-like grease structure. As a final step, the grease composition is subjected to a further blending operation, for example in a colloid mill having clearance of about 0.007, to increase the dispersion of the lithium 12-hydroxystearate soap particles. This dispersion can also be accomplished with a suitable high speed stirrer. The blending and milling operations employed in the preparation of the grease of our invention are those which are commonly employed in the manufacture of commercial lithium-base greases. When the grease mixture is heated at 320-340 F. to form the desired soap-oil dispersion and dehydrate the same the grease which is obtained upon cooling is a homogeneous mass having a gel-like grease structure. Further agitation or blending is employed to increase the dispersion of the fine soap particles and thus increases the yield and improves the properties of the grease. This blending step is not a true milling operation as used with other greases for reducing particle size or as is required in some cases to produce a homogeneous product.

Constituents (1) and (2) may be used in the ratio of 1:4 to 4:1 to each other and the total quantity of soaps which should be present to form the desired grease consistency should be at least about 5% by wt. preferably 7% by wt. or more. The total soap content of most standard greases is much higher, of the order of 15-30% by wt. Thus, our greases are less expensive to prepare, while still exhibiting superior properties even after long storage.

A suitable non-limiting example of the composition and process of our invention is set forth below:

A lard oil of the following specifications was reacted with 7.4% by wt. of flowers of sulfur at 330 F. to 340 F. until a clean copper strip immersed in the reaction mixture at about 300 F. for one minute, or at about 210 F. for 3 minutes, did not discolor beyond a grayish color (evidence of non-corrosivity of reaction mixture, that is, substantially all the sulfur introduced is bound by the fatty material). A tan color indicates active corrosivity, while no discoloration is optimal.

Lard oil specifications Titer C. Percent Sap. No. Iodine (extracted tree Pour Color Number fatty fatty Point NPA acid) acid 192-198 70-80 34-37 6-10 60 max. 6 max.

Assay of.sulfurized-phosphorized lard oil Properties:

Visc. at 210 425 S (percent by wt.) 7.4 P (percent by wt.) 0.23 Gravity 13 Approximately 4.5 parts by wt., based on final grease composition, of the extract obtained from the phenol extraction step during the manufacture of a high V.I. (80415.0) Mid-Continent Bright stock ubricating oil fraction was then introduced into an iron, open, grease kettle. This extract had the following characteristics:

Properties:

Gravity 13.3 Flash F.) 530 Fire F.) 610 SUS Visc. at 100 F. (extrapolated) 25,000 SUS visc. at 210 F 341 Viscosity Index 17 Color, NPA (dilute) 6 Pour Point, F. 65 S, percent by wt. 2.36 Neut. No. (1948) 3.16

Also introduced into the kettle was 28.45 parts by wt., based on final composition, of 160 viscosity Mid-Continent bright stock of the following assay:

Properties:

Gravity 25 Flash F.) 545 Fire F.) 615 SUS visc. at 210 F. 160 Pour Point, F Color, NPA 7 Viscosity Index 85 The mixture in the kettle was then heated and agitation appl'ed by means of a mechanical rotary stirrer. When the kettle contents reached 190 F., 6.31 parts by wt., based on final composition, of hydrogenated castor oil having the following specifications were added to the mixture:

At the same time 1.58 parts by wt., based on final composition, of constituent (2) as above-described in this example were also added to the mixture.

The contents of the kettle were constantly agitated and the temperature was increased to 200 F., at which point 1.32 parts by wt., based on final composition, of lithium hydroxide monohydrate in 1 part by wt., based on final composition, of water were added to the mixture under agitation. The mixture was then dehydrated at 320 F. for 1 hr. The heat was shut off and the resulting dehydrated grease was then out back with 28.44 parts by wt., based on final composition, of the above-described bright stock and 28.90 parts by Wt., based on final composition of 85 viscosity neutral lubricating oil of the following assay:

Assay of 85 viscosity neutral oil 6 When the temperature of the grease reached 240 F., 0.50 part by wt., based on final composition, of tetramethyldiaminodiphenylmethane was then added to the grease and the grease agitated until the additive was uniformly dispersed.

The grease was cooled to room temperature, then milled in a Charlotte Colloid Mill (laboratory model) at 0.007" clearance and 0.7 lbs./min. throughput.

The finished grease showed the following characteristics:

TABLE IV Properties of lithium-base extreme pressure grease A After 3 months After 24 (65 F.,

hrs. atm. pressure, in the dark) Properties E. P. properties:

Timken Test, 400 r.p.m., pass lbs 55 55 4-Ball E. P. Test weld pt., kgs 130 Penetration, ASTM:

Unworked. 357 360 Worked 354 358 Dropping point, F 376 374 Water Resistance, AN-G-5 (cup), 00.. 20 18 A second grease, grease B, was prepared of similar formulation to grease A except that the extreme pressure additive, sulfurized-phosphorized lard oil, was omitted. This grease had better water resistance (5 cc.), but a lower value in the Timken test, 400 rpm. (25 lbs). The dropping point was similar.

EXAMPLE II A second extreme pressure grease, grease C, with the same constituents used in Example I, was prepared according to the process of Example I and had the following formulation:

Grease C had a weld point of 136 kgs. in the 4-ball extreme pressure test, both before and after storage for 3 months at room temperature (65 F.) in the dark at atmospheric pressure.

It is seen that greases A and C showed no decreased extreme pressure properties on long-continued storage, as contrasted with the greases set forth in the data of the Boner reference, above cited.

In the preparation of our improved grease a combination of steps is used which is necessary to produce a satisfactory product. First of all, we use a combination of lithium soaps of (1) a hydroxy saturated C C fatty acid glyceride and (2) fatty acids produced by sulfurizing and phosphorizing non-hydroxy mono-unsaturated fatty acid glycerrdes prior to saponification. Secondly, formation of the soap-oil dispersion and dehydration of the grease mixture, following the saponification step, must be carried out in the temperature range of 320340- F. If the saponified grease mixture is dehydrated at tempera tures below about 320 F. an unsatisfactory grease structure is produced. If the grease mixture is heated to a temperature above 340 F., e.g., 350-400 F., for an extended period, either for in situ sulfurization or sulfurization-phosphorization of the unsaturated fatty acid soap or for dehydration of the product the soaps have been found to go into solution in the lubricating oil. When the mixture is cooled from such a high temperature the soap crystallizes from the solution and a heterogeneous hard grainy product (or in some cases a hard solid gel) is obtained which is not a true grease. If the grease mixture is dehydrated at 320340 F. a homogeneous grease having excellent E.P. properties is obtained.

Any modifications in the compositions, process, and apparatus for carrying out our process as are within the skill of one versed in the art are within the contemplated scope of our invention. This application is a continuation in part of our copending application Serial No. 546,818, filed November 14, 1955, now abandoned.

We claim and particularly point out as our invention:

1. An extreme pressure, lithium base grease with increased storage stability of extreme pressure properties which comprises a major amount of 'a mineral oil boiling in the lubricating oil boiling range, and a minor amount of a gelation agent, consisting essentially of a mixture of lithium soaps of group (1) saturated monohydroxy fatty acids having twelve to twenty-two carbon atoms in the carbon chain, and group (2) sulfurizedphosphorized non-hydroxy mono-unsaturated fatty acids having twelve to twenty-two carbon atoms in the carbon chain, the group (1) acids constituting approximately 80- 20 percent by weight of the mixed acids and the group (2) acids constituting approximately 2080 percent by weight of the mixed acids of said lithium soaps, the gelation agent being present in a sufiicient amount to produce a gelled grease structure, said grease being formed by the in situ saponification with lithium hydroxide of fatty material of the group consisting of glyceryl esters of group (1) acids and glyceryl esters of group (2) acids which have been sulfurized by reaction with elemental sulfur at about 330-340 F. and then phosphorized by reaction with a phosphorus sulfide at about 220-230 F. until substantially all sulfur and phosphorous were chemically bound, as measured by the copper-strip test, in lubricating oil, and followed by formation of a soapoil dispersion and dehydration of the dispersion at 320- 340" F., and cooling the product to produce a homogeneous gelled grease structure.

2. A grease in accordance with claim 1 in which said 8 gelation agent is present in the grease in an amount of at least about 5% by wt.

3. A grease in accordance with claim 1 in which a grease oxidation inhibitor is present in an amount of at least about 0.5% by wt.

4. A grease in accordance with claim 1 in which said group (1) acid is predominantly 12-hydr0xy stearic acid and said group (2) acid is predominantly sulfurizedphosphurized oleic acid.

5. A grease in accordance with claim 4 in which the group II acid ester is prepared by sulfurizing glyceryl trioleate with about 6-10% by wt. of sulfur and phosphorizing the same with about 0.21.0% by wt. of a phosphorus sulfide to passage of the copper strip test.

6. An extreme pressure, lithium-base grease in accordance with claim 1, characterized by increased storage stability of its extreme pressure properies and having the following formula:

Weight said grease being prepared by in situ saponification of the sulfurized-phosphorized lard oil and hydrogenated castor oil with the lithium hydroxide, followed by dehydration of the mixture at 320 340 F and cooling the mixture to produce a gelled grease structure.

References Cited in the file of this patent UNITED STATES PATENTS 2,441,587 Musselman May 18, 1948 2,450,254 Puryear et al. Sept. 28, 1948 2,651,616 Mathews .et a1. Sept. 8, 1953 FOREIGN PATENTS 704,788 Great Britain Mar. 3, 1954 716,968 Great Britain Oct. 20, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2359,1543 November 8, 1960 Thomas W. Mar-'tinek et a1.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters .Patent should read as corrected below.

. Column 8 line 26, in the table last column line 4 thereof, for "4500" read 4.50 a

Signed and sealed this 4th day of April 1961o (SEAL) Attest; ERNEST W. SWIDER ARTHUR w. CROCKER Attesting Ofiicer Acting Commissioner of Patents 

1. AN EXTREME PRESSURE, LITHIUM BASE GREASE WITH INCREASED STORAGE STABILITY OF EXTREME PRESSURE PROPERTIES WHICH COMPRISES A MAJOR AMOUNT OF A MINERAL OIL BOILING IN THE LUBRICATING OIL BOILING RANGE, AND A MINOR AMOUNT OF A GELATION AGENT, CONSISTING ESSENTIALLY OF A MIXTURE OF LITHIUM SOAPS OF GROUP (1) SATURATED MONOHYDROXY FATTY ACIDS HAVING TWELVE TO TWENTY-TWO CARBON ATOMS IN THE CARBON CHAIN, AND GROUP (2) SULFURIZEDPHOSPHORIZED NON-HYDROXY MONO-UNSATURATED FATTY ACIDS HAVING TWELVE TO TWENTY-TWO CARBON ATOMS IN THE CARBON CHAIN, THE GROUP (1) ACIDS CONSTITUTING APPROXIMATELY 8020 PERCENT BY WEIGHT OF THE MIXED ACIDS AND THE GROUP (2) ACIDS CONSISTING APPROXIMATELY 20-80 PERCENT BY WEIGHT OF THE MIXED ACIDS OF SAID LITHIUM SOAPS, THE GELATION AGENT BEING PRESENT IN A SUFFICIENT AMOUNT TO PRODUCE A GELLED GREASE STRUCTURE, SAID GREASE BEING FORMED BY THE IN SITU SAPONIFICATION WITH LITHIUM HYDROXIDE OF FATTY MATERIAL OF THE GROUP CONSISTING OF GLYCERYL ESTERS OF GROUP (1) ACIDS AND GLYCERYL ESTERS OF GROUP (2) ACIDS WHICH HAVE BEEN SULFURIZED BY REACTION WITH ELEMENTAL SULFUR AT ABOUT 330*-340*F. AND THEN PHOSPHORIZED BY REACTION WITH A PHOSPHORUS SULFIDE AT ABOUT 220*-230* F. UNTIL SUBSTANTIALLY ALL SULFUR AND PHOSPHOROUS WERE CHEMICALLY BOUND, AS MEASURED BY THE COPPER-STRIP TEST, IN LUBRICATING OIL, AND FOLLOWED BY FORMATION OF A SOAPOIL DISPERSION AND DEHYDRATION OF THE DISPERSION AT 320*340*F., AND COOLING THE PRODUCT TO PRODUCE A HOMOGENEOUS GELLED GREASE STRUCTURE. 